1. Field of the Invention
The present invention relates to an image forming apparatus, and more particularly to technology for improving image quality produced by an image forming apparatus based on an inkjet method which is equipped with a line head having a nozzle group in a two-dimensional matrix configuration, or a line head in which a plurality of head modules are joined together in a staggered matrix arrangement.
2. Description of the Related Art
Known image recording methods for an inkjet recording apparatus include a serial method (multi-pass method) which records an image while moving a recording head back and forth reciprocally in a direction perpendicular to the paper conveyance direction, and a line method (single-pass method) in which a long line head is arranged in the paper width direction which is perpendicular to the paper conveyance direction and an image is recorded by one image recording pass by the line head.
Japanese Patent Application Publication No. 4-110154 discloses a composition in which a hole or a projection is provided in both end portions of a paper conveyance device, as a device for positioning and securing a recording head accurately with respect to a paper conveyance device, and the position of the conveyance device in the axial direction (horizontal direction) is restricted by providing projections or holes in the line head side.
Japanese Patent Application Publication No. 2005-138371 discloses a composition in which a position restricting carriage pin is provided in a carriage on which a group of a plurality of ink heads is mounted, and a positioning pin is provided in a belt platen which supports an endless belt that conveys paper, whereby the positional relationship therebetween is restricted due to the carriage pin fitting into the positioning hole.
Japanese Patent Application Publication No. 2009-292044 proposes positioning a recording head unit in which a plurality of recording heads are arranged and secured with respect to a paper conveyance unit, by means of pins and pin holes, in addition to which the recording head unit is fixed in an integrated fashion to the conveyance unit by gripping the pins which have been inserted into the pin holes, by means of a collet chuck. It is stated that, according to a composition of this kind, even if the apparatus is affected by vibration during operation of the printer, the conveyance unit and the head unit perform exactly the same vibration, and therefore the accuracy of the depositing positions is maintained (Paragraph 0041 in Japanese Patent Application Publication No. 2009-292044).
In each of Japanese Patent Application Publication No. 4-110154, Japanese Patent Application Publication No. 2005-138371 and Japanese Patent Application Publication No. 2009-292044, the ink deposition accuracy may decline due to relative vibration between the line head and the paper, and there is a possibility that the image formation lines (raster lines) in the paper conveyance direction are skewed. The amount of skew (amplitude) which is perceived as a problem in these related art technologies is based on a vibration level of the order of several tens of μm.
However, apart from the technical problems described in Japanese Patent Application Publication No. 4-110154, Japanese Patent Application Publication No. 2005-138371 and Japanese Patent Application Publication No. 2009-292044, a line head having a nozzle group in a two-dimensional arrangement or a line head formed by joining together a plurality of head modules in a staggered matrix configuration also involves problems of the following kinds.